There are three types of torques produced in a HDD VCM, namely, yaw, pitch and roll torques, as shown in FIG. 1. Yaw torque produces useful work and is the intended mechanical output of the VCM, whereas pitch and roll torques are undesired by-products which can cause serious resonance issues. These resonances can result in HDD failure.
In order to limit the number and magnitude of the resonances, it is useful to quantify the pitch and roll torques. Commercially available three axis load cells, while conceptually possible, have not been successful measuring pitch and roll torques in a HDD VCM. Two issues prevent its use. Firstly, the resolution is not adequate to accurately measure these small pitch and roll torques. Secondly, sensors used by the three axis load cell require that the yaw torque does not exceed several times of the pitch and roll torques. If this condition is not satisfied, the high yaw torque will corrupt the low pitch and roll torques, thus resulting in non-accurate measurement of the pitch and roll torques.